This invention relates to the general field of acoustic imaging, and in particular, to highly sensitive systems and apparatus for detecting and displaying orthoscopic acoustic images.
The use of ultrasonics to nondestructively and noninvasively inspect objects and bodies for internal discontinuities, irregular shapes, etc., is well known in both the industrial and medical fields. This invention deals with the formation of orthoscopic or two dimensional images on a liquid crystal cell rather than the formation of holographic or three dimensional images.
In one form, ultrasonic imaging is accomplished by using electronic displays in which the ultrasonic signal is electronically detected (by a piezoelectric detector array) and enhanced. Green, P. S., Schaefer, L. F., Jones, E. D., Suarez, J. R., A New Performance Ultrasonic Camera, in Acoustical Holography, Vol. 5, Ed. Green, P. S., Plenum Press, New York 1974, 493-503.
In another form, the ultrasonic image is proposed to be detected and displayed using a liquid crystal cell which includes a pair of cover plates between which a layer of liquid crystal material is encapsulated. See, for example, Greguss, U.S. Pat. No. 3,831,434; and Dion, U.S. Pat. No. 4,338,821. The performance of liquid crystal cells may be enhanced by treating the liquid-crystal-contacting surfaces of the cell with a surfactant, such as lecithin. It is also known that liquid crystal materials will respond to externally applied force fields. See, for example, Greguss; Dion; Tsunoda et al., U.S. Pat. No. 4,035,060; Mailer, U.S. Pat No. 3,837,423; and "New Techniques of Acoustic Image Detection," Mailer et al., International Journal of Non-Destructive Testing, 1973, Vol. 4, pp. 283-299. Introduction to Liquid Crystals Ed. E. B. Priestly, Peter J. Wojtowicz, Ping Sheng. Plenum Press June 1976.
Liquid crystal detector cells may be preferred to fully electronic detection and display systems, since liquid crystal cells can be less expensive to manufacture and maintain than fully electronic systems and can provide substantially instantaneous well-resolved images without the need for electronic image enhancement, through complicated signal processing, or adjustment.
The use of ultrasonics in medical applications, is increasing, and in such applications, it is particularly desirable that the intensity of the insonifying ultrasonic field (i.e., the beam incident on the patient) be at the lowest possible level. In order to be useful in a wide range of such applications, the liquid crystal cell must be able to detect ultrasonic fields that have passed through or have been reflected from the body or organ to be examined.
In present medical applications the insonifying acoustic field has a maximum intensity on the order of 100.times.10.sup.-3 w/cm.sup.2. It is known that in human tissue there is a loss of ultrasonic intensity of about 3 db per centimeter of tissue penetrated. Thus the intensity of the imaging acoustic field exiting the patient is much less than 10.sup.-3 w/cm.sup.2. For example, in order to penetrate a 10 cm thick tissue, there would be a loss of ultrasonic intensity of 30 db. Therefore, if the incident intensity is 100.times.10.sup.-3 w/cm.sup.2 the exiting intensity will be about 100.times.10.sup.-6 w/cm.sup.2. Present orthoscopic imaging systems using liquid crystal cells can not detect a field and display an image where the incident acoustic intensity is much less than 10.sup.-3 w/cm.sup.2.
Thus prior liquid crystal detecting cells are not capable of detecting and displaying an image from the low acoustic intensity beams that exit an examined object.
It is therefore an object of this invention to provide a liquid crystal-type detector cell for use in an orthoscopic ultrasonic inspection system, of the type used in medical diagnosis, which can detect low intensity acoustic fields.
It is another object of this invention to provide an orthoscopic liquid crystal-type ultrasonic inspection system which is capable of detecting and displaying ultrasonic fields having intensities less than about 10.sup.-3 w/cm.sup.2.
These and other objects of this invention will become apparent from the following description and appended claims.